Fixed type error in generator for split-at-any and split-at-first-of-any
Fixed the bug in split-at-any and split-at-first-of-any where they
could not handle patterns containing character with special meanings
in regexps.
Added unit tests for the split commands, and extended the
unit test framework to handle blocks with dropdown operators.
Created a separate class for Blockly Code Generator Tests.
Changed split (only split, not splt-at-any, etc.) so that there
is no trailing empty-string in the result, when "splitting" at the
final character in the string.

Change-Id: I1b48e4de8da98bbfae845a22642f42c349600db0